When blasting a tunnel, bolts are mounted in the inner wall for various reasons. The bolts can, e.g. be used for stretching a water tight membrane. They can also be used as crash protection or as protection against landslide. Even if a certain shape is planned, during blasting, the cavity forming the tunnel does not necessarily gain the shape planned. This can be compensated for by, e.g., setting bolts of greater or smaller length. However, bolts of greater lengths might easier break if run into. To mitigate this one might measure the lengths of the mounted bolts and then make some of the bolts more rigid. This is however usually not performed since the work to check about 10 000 bolts is insurmountable.
When mounting the bolts all the holes for the bolts are bored in accordance with a predetermined project plan. After that, construction workers use aerial work platforms to gain the right height and manually fill the bore holes with grout and insert bolts in the holes. Naturally, this work is hard and takes time and the bolts and the grout are heavy. Furthermore, the risk of the people making errors is quite high. Instead of grout, chemical anchors can be used which however are expensive. Alternatively, expanders can be used but expanders do not provide satisfactory attachment.
WO 2013/098460 and WO 2013/098459 each relate to a method for drilling holes in a tunnel, and post-processing of the pre-drilled holes. During drilling, positioning data of the hole is gathered and stored in a control unit. The stored positioning data is used when rough positioning a post-drilling unit in a vicinity of a pre-drilled hole. The positioning also comprise a fine positing wherein the hole collar is detected and the insertion device is driven from the vicinity to the collar. In WO 2011/104441 a rock drilling rig comprises a drilling unit for drilling drill holes in a drill hole pattern. The location of the drilling unit is determined and a control unit is arranged to control (by means of a control member) on the basis of a given target position, actuators influencing the position of the drilling unit. The number, depth, diameter, start locations and directions of drill holes may be determined in a reinforcement pattern, which represents one form of drilling patterns. The reinforcement drill holes may be drilled in fan form, whereby there are drill holes on both walls and on the ceiling of the tunnel.